Pile Design and Construction Practice, Fifth edition

9.6 Piled foundations for over-water bridges

9.6.1 Selection of pile type

Because of the desirability of avoiding different types of piling on the same bridge project
the piling used for piers constructed in over-water locations will usually dictate the type to
be used for the abutments. Driven piles are the favoured type for over-water piers. The
installation of bored piles is limited to work carried out either in a pumped-out cofferdam,
or in a permanent casing driven below river bed. In fast-flowing rivers the casing will have to
be taken down to a sufficient depth below the river bed to obtain fixity against overturning
particularly in conditions of bed scour. Tubular steel piles or precast concrete piles of cylin-
drical section are preferred to H-sections in order to minimize current drag and eddies
causing bed scour. The need for raked piles for efficient resistance of lateral forces again
favours a driven type of pile. Where precast prestressed cylindrical piles are used in
deep-water locations or for deep penetrations below bed level there can be problems with
handling long heavy piles. Also, forming joints to extend partly driven piles can cause
difficulties and delays.
Attrition by soil particles of the exterior surface of piles at the sea or river bed can be
a factor influencing the material of the pile and its wall thickness. This is more likely to be a
problem where the bed level is constant or changing over a limited range rather than rivers
where seasonal floods cause wide variations in bed contours.

Miscellaneous piling problems 463

Figure 9.21Arrangement of settlement reducing piles beneath bridge approach embankment (after
Reid and Buchanan (9.31)).

PF ash fill

Terram fabric reinforced with

‘Paraweb’ strapping

Cross section A-A

A

PF ash fill

Reinforced fabric

Reinforced concrete pile caps

General fill

Soft alluvium

Precast concrete piles

Transition piles

Embankment support piles

Bridge abutment

support piles

A